The standardized ileal amino acid (AA) digestibility (SID) of 3 cereals: wheat, barley and maize; 3 feeds with a medium protein content: faba beans, field pea and full-fat rape seeds; and 4 by-products: solvent-extracted rapeseed meal (RSM), rapeseed expeller cake (RSC), maize distillers dried grains with solubles (DDGS) and soyabean meal (SBM) was measured in 30-day-old broiler chickens. Digestibility values were determined with the direct method using semi-synthetic diets containing Cr2O3 as an indigestible marker. Each diet was offered ad libitum for 5 days to 4 replicate cages of 6 broilers and the ileal contents were collected by the slaughter method. A protein-free diet was fed to assess ileal endogenous AA losses (IEAA). These IEAA values were used to obtain SID coefficients for each of the tested ingredients. Considering the SID values of 14 of the most important AA, the test ingredients were ranked as follows. Within cereal grains: maize > wheat > barley. The exception was the SID of cysteine in maize which was lower compared with that in wheat. Within native seeds: faba beans = peas > rape seeds. However, the SID of methionine was greater in rape as compared with legume seeds. Within by-product feeds: SBM > RSC > RSM > DDGS. However, SID values for valine, phenylalanine and serine in DDGS were comparable to those obtained for SBM and higher than in the two rapeseed products.

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